112 
taken, and whicli were found by Mr, Augustus Jessup. It is 
distinguishable from C. similis by its more rhomboidal form. 
C'YCLAS PARTUMEIA. — Shell thin and fragile, transversely*sub- 
orbicular, with small, irregular, inequidistant, concentric wrinkles, 
and larger adventitious undulations; base rounded; anterior and 
posterior edges nearly central; hinge teeth prominent and distinct; 
lateral teeth prominent, white ; within impressed by the exterior 
undulations, and bluish-white on the margin and submargin. 
Length nine-twentieths; breadth eleven-twentieths of an inch. 
This species was found by Mr. William Hyde, in a pond near 
dermantown, in plenty. In comparison with C. similis^ it is 
thinner, more transparent, not flattened at base, more obtusely 
rounded each side, and instead of grooves of some degree of regu- 
larity as in that shell, it is sculptured with irregular wrinkles and 
waves. Mr. Hyde took fifty young ones out of a single specimen* 
N. B. The genus Cyclas was inserted into this essay inad" 
vertently ; the species, however, are new.^ 
[*The title of tlie paper being “ Description of Univalve, &c., Shells* 
—Ed.] 
[J. A. N. S. vol. iv. p. 368, et seqq., 1825.] 
Modiola. — Amongst a number of marine shells from the island 
of Minorca, presented to the Academy by Dr. Alexander Mont- 
gomery, of the U. S. Navy, is a single valve of the Pecten nodosus^ 
Linn., on which were several elevations that, on a cursory glance, 
presented an appearance not unlike the Balanus. On a more par- 
ticular inspection, each elevation proved to be similar to the others 
in form and consistence, and to be composed of fine dark colored 
sand, agglutinated together, attached by a broad base to the surface 
of the Pecten, and rising in the shape of a very low cone around 
an included shell, the visible portion of which is exactly cordate. 
Having carefully detached the mass, I found the imbedded shell 
to be a Modiola j closely allied to the discors, Gmel., with its byssus 
very firmly affixed to the supporting surface. 
The following is a description of this shell : 
Modiola opifex.-— O val, reddish-brown; anterior hinge-mar- 
gin flattened, cordate ; within iridescent. 
Base contracted behind the middle, the contraction not wide 
